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I'm working on my first two builds (classical -two in case of the fatal flaw), and am ready to attach the sides to the tops. Next I'll be closing in the box, but just realized (better late than never) that I don't know if I need to finish the inside of the box in any way. What does anyone out there recommend? The tops are spruce and red cedar and sides and bottoms are zebrawood and mahogany, if that makes a difference. I've used spruce for braces and mahogany for kerfing. Thanks in advance for any advice!

The overwhelming majority of makers do not finish the inside of the box. It certainly isn’t necessary and it could make future repairs difficult.

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Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I seem to recall there were at least a couple of threads on this. Below is one.

viewtopic.php?f=10101&t=25066&hilit=Taran+inside

Sandpaper, up to P240 at least.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

No .

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I recently began shellacking the inside of the tops to see if it would help prevent the tops from moving up and down (changing the action) during RH swings. It made no difference...

yes, always, shellac

+1

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Dave
Milton, ON

I can't fit my hand, and spray gun though the soundhole

Seriously, I have finished the inside with shellac a few times, but no longer do. I don't see any big drawbacks, but didn't think there was any advantages either.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

No. It does little, if anything, to slow moisture exchange. It does however, hide glue squeeze-out that was not cleaned up very well. Many different opinions, though.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

I've seen this discussed and argued many times. I believe most makers don't apply a finish inside, as they are convinced this could make future repairs more difficult (I presume they are talking about gluing in cleats, replacing braces and so forth.

On the other hand, I can hardly believe that a thin coat of shellac sealer would be any more difficult to clean up than a failed brace glue joint or thirty years worth of dirt and oxidation. No matter what's inside the box, it must be cleaned up before a repair can be made.

I'm an archtop fan and I've watch Robert Benedetto demonstrate sealing the inside of his archtops with a thin coat of shellac, which he immediately wipes off with a paper towel. He will remove the backs of his instruments for repair work, whereas a classical builder will work through the sound hole if possible.

I am NOT arguing for an internal finish when I say all this. I'm just saying that I think a lot of people repeat what they have read, without having personal experience.

I don't have that repair experience. I've only got logic and an inquisitive mind. I would love it if an experienced repair person would chime in and detail this for us, and explain it once and for all. I would really listen to that. I really would, so I hope someone can definitively explain this. I'll be watching with you.

Patrick

this is one of those things that matters to those that do it but it only adds a cost to the construction and there is no real advantage to doing it.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Shellac, yes. Makes a huge difference in humidity exchange. Taking a guitar from a controlled environment to a less controlled environment my last four guitars are much more stable than my first nine. Especially if you build in the southeast U.S., epicenter of humidity swings. T

Somogyi recommends a coat of shellac, but seeing as this is your first build, I'd think you have much bigger things to worry about

Relax and think about it for number 10.

Steve

The effectiveness of shellac would likely depend on whether it's waxed or dewaxed.

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David Malicky

How so David?

+1

I've added shellac to the inside of a few guitars because the customer requested it. It's sometimes useful to make things look cleaner but I highly doubt it helps much against low/high humidity. In terms of repairs, the wood should be sanded anyway as oxidized wood does not bond that well.

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Build log

All,
appreciate such prompt replys and suggestions. Charles T, thanks for the thread. Think I'll go with some additional sanding and leave it at that for now; I'm getting anxious to close the boxes and see how this binding thing goes.
Again, thanks everyone.

Shellac is not water proof so if will allow water to pass. I don't see from an engineering standpoint other than looks. It may help for RH shock but not as a true moisture barrier.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I have done it a couple of times, with shellac. It takes no time at all and costs very little. I think it makes the inside of the box look cleaner - especially with dark woods like walnut or rosewood. I am sure it does absolutely nothing for RH stability, sound quality or anything else except appearance.

Shellac is one of the best vapor barriers we have. I'm still looking for the link but 3 coats of shellac beats just about everything when it comes to passing moisture.

I put about 3 coats of shellac on the interiors of my instruments now and I'm finding that rapid changes in humidity are more gentle on the instrument now. They still swell when it's wet but they now do so more evenly on the inside and out.

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Yay, after two years of re-googling I finally found the study I was talking about. http://www.fpl.fs.fed.us/documnts/fplrp/fplrp462.pdf

I was wrong about shellac being the best but it's still very good compared to most other finishes.

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I never have but I've always wondered if it would be better.

For those that say it won't make a difference? Why bother finishing the outside of the guitar then?

Is finish really just to enhance beauty? Isn't it also functional too? Doesn't it slow the absorption of moisture into the wood?

It certainly can depending on the finish.

The reason I finish the insides is to even out the absorption. Shellac is a wonderful moisture barrier and many of us use shellac as a base coat under other finishes (I do). After having some instruments go all pringly on my in high humidity environments I started shellac-ing the insides and it's made a difference. With shellac on one side and nothing on the other, you get quick moisture absorption on one side and slow on the other which can cause major distortion.

By sealing both sides with shellac, you're balancing out the absorption. If your finish is transparent to moisture, it will make much less of a difference. Check the link I posted above to see how your finish fares.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com